Research On Microstructure And Properties Of Mg-Re-(Al) Alloys With High Thermal Conductivity

Magnesium alloys are the lightest metal structural materials and have high specific strength,specific stiffness and good thermal conductivity.With the trend of lightweight and portable in the electronics and automotive industry,as well as the demand for thermal performance of materials.It is of great significance to design magnesium alloys with excellent mechanical properties and thermal conductivity.In this paper,La series elements and Gd element are selected as the main alloying elements,the rare earth magnesium alloys include two systems,Mg-RE binary alloys and Mg-Al-RE ternary alloys.Permanent mold direct-chill casting method was used to obtain the alloys.The microstructure,thermal conductivity test between 30?-240?,and mechanical properties test of as-cast state were investigated.In order to improve the strength of the alloys,homogenization treatment and extrusion deformation of as-cast alloys have been carried out,the effect of heat treatment and extrusion deformation on the microstructure,thermal conductivity and mechanical properties of the alloys were analyzed.The effect of the RE elements on the microstructure,thermal conductivity and mechanical properties of as cast and as-extruded Mg-RE binary alloys have been investigated.With the increasing of RE content,grain size of the as-cast Mg-RE alloys decrease,the yield strength(YS)increase,the thermal conductivity decrease.The mechanical properties of as-cast Mg-RE alloys are low.After extrusion,the grain size of Mg-RE alloys are obviously refined,and the thermal conductivity of the alloys are obviously anisotropic.The thermal conductivity in the vertical extrusion direction is higher than that in the parallel extrusion direction.After extrusion,the strength of MgRE binary alloys increases by 4-5 times compared to the as-cast srate,and the elongation increases also.The extruded Mg-3.7La alloy has the best comprehensive properties without any heat treatment process.Its yield strength is 356 MPa,tensile strength is 378 MPa,elongation is 6%,and the thermal conductivity is 132W/m·K in the parallel extrusion direction,136W/m·K in the vertical extrusion direction.After homogenization treatment,the plasticity of Mg-5.2Gd alloy which extruded at 400 ? has been greatly improved,and its elongation has been increased by 5 times.The microstructure and properties of as-cast and as-extruded Mg-Al-RE ternary alloys with the fixed Al content has been investigated.It is found that the content of second phase and thermal conductivity increases with the increase of RE content but grain size decreases.After extrusion,the thermal conductivity of Mg-Al-La alloys increased,The thermal conductivity in the vertical extrusion direction is higher than that in the parallel extrusion direction.However,the thermal conductivity of as-extruded Mg-Al-Gd alloy are lower than that of as-cast state,and the thermal conductivity in the direction of vertical extrusion is basically the same as that in the cast state.After extrusion,the mechanical properties of Mg-Al-RE alloys were improved significantly and the mechanical properties of Al La series alloys increase greatly.Compared to the as-cast state,the yield strength and tensile strength of the extruded AlLa45 alloy increase by 170 MPa,and the elongation increases by 9%.The mechanical properties of the as-cast Mg-Al-Gd alloys have been good,and the strength of the Mg-Al-Gd alloys isn't greatly increased after extrusion.Explored the influence of Ca element and Sr element on the microstructure and properties of as-cast and as-extruded Mg-4Al-5La alloy.It is found that the volume fraction of the second phases in the as-cast and asextruded alloys decreases as the Ca and Sr elements are added,and there are black blocky phases between the grains.The thermal conductivity of the as-cast and as-extruded alloys decreases slightly.Compared with the as-cast state,the addition of Ca element has a more positive impact on the mechanical properties of the extruded Mg-Al-La alloys,the mechanical properties of the extruded AlLaX4504 alloy are better than the extruded AlLa45 alloy,and the yield strength increased by 36 MPa,tensile strength increased by 10 MPa,and elongation increased by 3% after microalloying.However,the mechanical properties of the extruded Al LaJ4504 alloy decrease compared with the AlLa45 alloy.